1. Field of the Invention
The present invention relates, in general, to data communication, and, more particularly, to a system, method and architecture for managing multiple low bandwidth connections over a single higher bandwidth communication channel.
2. Relevant Background
Enterprise computing networks are formed by a geographically distributed collection of computing resources that are linked by high speed communication channels. Typically, one or more mainframe computers are used to supply bulk data processing while other nodes are used for specialized functions. An example is a storage area network (SAN) in which mass storage is implemented in a xe2x80x9cstorage farmxe2x80x9d that is coupled to the mainframe processors by a communication channel or network.
As used herein, a communication xe2x80x9cchannelxe2x80x9d provides direct or switched point-to-point connection between communicating devices. A circuit switched channel is typically hardware intensive and transports data at high speed with little overhead required for channel management. Circuit switched connections usually remain established even if no data is being transferred, thus bandwidth is wasted, yet may support multiple users through multiplexing techniques such as time division multiplexing.
Packet switched networks on the other hand allow users to dynamically share the network medium and available bandwidth using variable-length packets. Packet switched networks are characterized by more efficient and flexible data transfer as compared to circuit switched communication. Packet switched communications increases the overhead by adding addressing information to each packet that enables the packet to be switched between various network components until the destination is reached.
Early efforts to implement high bandwidth long distance communication used switched circuit technology. A widely used example of such technology is the singlebyte command code sets connection (SBCON) architecture. SBCON is standardized by American National Standards Institute (ANSI) standard X3.296-1997 entitled xe2x80x9cInformation Technologyxe2x80x94Single-Byte Command Code Sets CONnection (SBCON) Architecturexe2x80x9d. ANSI document X3.296-1997 describes an input/output (I/O) and interconnection architecture that specifies fiber optic links, switched point-to-point topology, and I/O protocols for high bandwidth, high performance and long distance information exchange. As used herein, SBCON refers to standard SBCON architecture as well as variants of SBCON such as the enterprise system connection (ESCON) architecture offered by IBM, and the like. For purposes of the present invention these variants are considered equivalent to SBCON.
SBCON supports a maximum of 200 Mbit/second full duplex channels. SBCON has been widely deployed to support communication between mainframes and storage devices or other peripheral components in a distributed architecture. Hence, there exists a significant installed base of SBCON applications and devices. However, the rapid advances of communications and data processing and storage technology have made many SBCON installations non-optimal.
Distributed computing environments in general and SAN applications in particular require increasingly higher speed communications links between devices. Conventional mainframe architectures support an operating system defined, system limited number of connection ports (e.g., 256) for connections between the mainframe and other devices. Performance improvements in data processing speeds have spawned increasingly dataintensive and speed-sensitive applications. As the demands for data transfer have increased, the 200 Mbit/second per channel limitation of prior communication technology is limiting. As the mainframe operating system cannot be readily changed to provide more ports, the only solution for increased data transfer is to increase the bandwidth of each channel.
Fibre channel has been developed as a extensible, flexible data communication architecture for high bandwidth data transfer between workstations, mainframes, supercomputers, storage devices, and other peripherals. Fibre channel operates at a variety of speeds ranging from 256 Mbits/second (bi-directional) to 2 Gbits/second (bi-directional) with speeds of up to 4 Gbit/second contemplated. Standards are defined for both copper and optical communication media. Fibre channel combines desirable features of both packet switched and circuit switched communication. Fibre channel uses an active, intelligent interconnection architecture that called a xe2x80x9cfabricxe2x80x9d to connect devices. While the physical implementation of Fibre channel is packet switched, a fabric supports varying classes of service, including dedicated virtual connections between nodes, to ensure efficient transmission of different types of traffic.
The fabric provides a number of ports, called F_Ports, that enable devices to access the fabric. Devices couple to an F_Port using a node port (N_Port) implemented within or associated with the device. To connect to a fibre channel fabric devices include a node port or xe2x80x9cN_Portxe2x80x9d that manages the fabric connection. The N_port establishes a connection to a fabric element (e.g., a switch) having a fabric port or F_port. Devices attached to the fabric require only enough intelligence to manage the connection between the N_Port and the F_Port. Fabric elements include the intelligence to handle routing, error detection and recovery, and similar management functions.
A switch is a device having multiple F_Ports where each F_Port manages a simple point-to-point connection between itself and it""s attached system. Each F_Port can be attached to a server, peripheral, I/O subsystem, or bridge. A switch receives a connection request from one port and automatically establishes a connection to another port based on address information contained in the request. Multiple calls or data transfers happen concurrently through the multi-port fibre channel switch. A key advantage of switched technology is that it is xe2x80x9cnon-blockingxe2x80x9d in that once a connection is established through the switch, the bandwidth provided by that connection is not shared. Hence, the physical connection resources such as copper wiring or fiber optic cabling can be more efficiently managed by allowing multiple users to access the physical connection resources as needed.
Although fibre channel offers much higher bandwidth connection technology, the large installed base of legacy circuit switched systems such as SBCON devices cannot directly connect to a fibre channel fabric. While it is feasible to offer a fibre channel port to a mainframe computer in a network, there may be many hundreds of node devices that would need to be upgraded or replaced interface with the fabric. As a result, migration to higher speed technology afforded by fibre channel has been slow and too expensive to implement in some instances.
Efforts have been made to encapsulate or embed SBCON and ESCON traffic in fibre channel packets. These solutions make SBCON traffic compatible with fibre channel communication media. However, so long as the high bandwidth fibre is supplying data to an SBCON device, the fibre channel communication link can only operate at an effective data rate equal to what the SBCON device accepts. Hence, much of the benefit of fibre channel is wasted when accessing legacy SBCON or ESCON devices. Accordingly, there is a need for a connection architecture that enables a high speed communication link such as fibre channel to carry low bandwidth connections in an efficient manner.
Briefly stated, the present invention involves a bridge circuit for a communication link having a packet switched side supporting a full duplex packet switched link and a circuit switched side supporting a number of full duplex circuit switched links. A binding mechanism within the bridge circuit maintains a data structure for storing a logical binding description. The logical binding description binds packet switched frames to a particular one of the circuit switched links.
The present invention also involves a data communication architecture including a plurality of devices having input/output (I/O) ports supporting communication at a first rate and a data processor having a number of I/O ports where each I/O port supports data communication at a second data rate. The second data rate is at least double the first data rate. A communication link coupled to one of the data processor I/O ports supports the second data rate. A bridge device is coupled to the communication link and to the I/O ports of the plurality of devices. The bridge device translates the communication link at the second data rate to a plurality of communication links at the first data rate, where the plurality of communication links at the first data rate are substantially independent of each other (i.e., the first data rate links are not required to share control, signaling, or data information).
In another aspect, the present invention involves method for operating a communication link with a bridge unit supporting a high bandwidth connection and a plurality of low bandwidth connections. Operability of the low bandwidth connections is verified and an exchange credit value is determined based on the number of operable low bandwidth connections. A message including the credit value is issued on the high bandwidth connection. Any device coupled to the high bandwidth connection is required to have at least one exchange credit before communications will be accepted by the bridge unit on the high bandwidth connection from that device.